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Christopher Osburn


Jordan Hall 4150


Chris Osburn is Professor of Marine Biogeochemistry in the Department of Marine, Earth, and Atmospheric Sciences at North Carolina State University. Previously, he was a Research Chemist at the United States Naval Research Laboratory. His research interests span carbon and nitrogen cycling across the aquatic continuum and focus on the biogeochemistry of organic matter in surface waters and how optical and chemical properties of organic matter can be used to understand global change. Over the past 10 years he has studied the biogeochemical consequences of extreme weather events on coastal waters; impacts of organic matter sources on coastal water quality; effects of sea level rise on organic matter fluxes from tidal wetlands; and formation of recalcitrant organic matter in the ocean. Recent interests have focused on reuse of data in support of entrepreneurship related to economic development for sustainable and resilient coastal communities.


Interested in collaborating with people working in:
Sustainable agriculture, forestry, and rural, natural resource-based economies; Coupled human and natural systems; and Mutually beneficial engagement that emphasizes social equity.


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Date: 12/01/20 - 12/01/22
Amount: $134,795.00
Funding Agencies: National Pork Board

All livestock operations generate fecal waste and manure management is an essential aspect of pork production. Regulations mandate permitting, training, design specifications, soil testing and livestock operation stream vegetation buffers. As the scale of pork production has increased to meet consumer demand communities have heightened their concern about the environmental impact of pork operations. Pork producers are actively working to reduce their overall water usage, land use and the carbon foot-print of their farming operations. Responsible environmental farm management has become an inherent necessity to maintain the sustainability of the pork industry and pork producers in the US have affirmed their obligation to safeguard our natural resources and manage pork production operations in a manner that protects natural environments and public health. The proposed studies support environmental management of pork production and address community concerns by facilitating accurate detection and effective attribution of the origin of fecal waste in surface waters and groundwater.

Date: 10/01/21 - 9/30/22
Amount: $57,000.00
Funding Agencies: National Pork Board

Livestock operations generate fecal waste and manure management is an essential aspect of livestock production. Local and state regulations mandate permitting, training, design specifications, and stream vegetation buffers between livestock operations and surface waters. The scale of pork production has increased to meet consumer demand and as production facilities have grown, communities have heightened their concern about the environmental impact of pork operations. Pork producers have worked effectively to reduce their overall water usage, land use, and the carbon footprint of farming operations (National Pork Board, 2018, Thoma et al. 2011). Responsible environmental farm management has become a business necessity for pork producers in the US and producers have affirmed their obligation to manage pork production operations in a manner that protects natural ecosystems and public health. Watersheds, however, generally support multiple types of livestock operations and human dwellings. Each livestock enterprise and residential community is a potential source of fecal waste in surface waters. Fecal waste in surface waters is generally referred to as non-point source contamination. In reality, all fecal waste has a vertebrate animal origin and the species of origin varies with adjacent land-use practices. Monitoring programs established to protect public health have traditionally relied on the culture or detection of fecal coliforms, total coliforms or Enterococcus bacteria in water samples as indicators of fecal contamination in surface waters. These enteric organisms are non-specific indicators of the presence of fecal waste but do not attribute contamination to specific animal hosts. The detection of host-specific enteric organisms, such as Bacteroidales spp. and genetic assays focused on detecting these microbial species have been developed as alternatives to non-host specific indicator organism detection methods (Harwood et al. 2009). All vertebrates release cells from their gastrointestinal tract in their feces. These cells contain mitochondrial DNA (mtDNA), a routine aspect of forensic investigation that can be applied to identify the animal hosts associated with fecal waste (Caldwell et al. 2007). The detection of mtDNA is highly host specific. If mtDNA is detected in a water sample, the vertebrate animal associated with that mtDNA can be determined. Initial studies, however, lacked sensitivity (Caldwell et al. 2009). When we initially developed and tested these assays, at times, fecal waste was present in a stream but not detected. In studies supported by the National Pork Board, we refined these initial mtDNA assays by adapting the use of new Droplet digital PCR technology (BioRad Inc., California, USA), which markedly enhanced the sensitivity of the assay for identifying the presence of host mtDNA in surface waters. New primers and probes were designed, and the assay proved both sensitive and specific. Our studies confirmed the presence of fecal contamination in Stockinghead Creek in Duplin County, NC and documented that the fecal contamination in the creek originates from at least four species, cattle, humans, poultry and swine. This proposal focuses on addressing concerns about the origin of fecal waste in surface waters in other North Carolina livestock intensive watersheds. Specific objectives include: 1) Attributing the source of fecal contamination in NC surface waters in Duplin and Sampson County, NC watersheds ; and 2) Responding to concerns about fecal contamination.

Date: 05/01/19 - 1/01/21
Amount: $95,760.00
Funding Agencies: National Pork Board

All livestock operations generate fecal waste and manure management is an essential aspect of pork production. Regulations mandate permitting, training, design specifications, soil testing and livestock operation stream vegetation buffers. As the scale of pork production has increased to meet consumer demand communities have heightened their concern about the environmental impact of pork operations. Pork producers are actively working to reduce their overall water usage, land use and the carbon foot-print of their farming operations. Responsible environmental farm management has become an inherent necessity to maintain the sustainability of the pork industry and pork producers in the US have affirmed their obligation to safeguard our natural resources and manage pork production operations in a manner that protects natural environments and public health. The proposed studies support environmental management of pork production and address community concerns by facilitating accurate detection and effective attribution of the origin of fecal waste in surface waters and groundwater.

Date: 04/16/18 - 3/31/20
Amount: $39,999.00
Funding Agencies: US Dept. of Interior (DOI)

Freshwater mussel populations throughout North America have declined precipitously during the last three decades. Captive propagation and release of the captive reared stock has become an integral component of efforts to mitigate the decline and augment the reproductive capacity of remaining populations. Freshwater mussels are reared in captivity using two alternative approaches that focus on different approaches to facilitating the metamorphosis of juveniles. Either host-fish are used to support the metamorphosis of the larval stage or the larvae are reared in vitro in petri dishes and the metamorphosis is nutritionally supported with culture media. The initial survival of in vitro reared mussels is poor and their initial growth lags behind that of host-fish reared animals. Our limited understanding of the nutritional needs of freshwater mussels and how specific components of their diet contribute to their nutritional health impedes our ability to sustain them in captivity. In addition, declines noted in some free-ranging populations appear to be associated with poor nutrition. We propose studies to further inform our understanding of the role of different food-web resources in the diets of freshwater mussels. Specific objectives include: 1) Examining the role of pollen in the diet of freshwater mussels; 2) Assessing the role of detritus in freshwater mussel diets; 3) Quantifying the filtration ability of selected freshwater mussels species; 4) Preliminary studies of diet and freshwater mussel nutritional health; and 5) Refining procedures for characterizing the chemical composition of freshwater mussel shells.

Date: 02/01/18 - 1/31/20
Amount: $14,684.00
Funding Agencies: NCSU Sea Grant Program

A nitrogen (N)-based Total Maximum Daily Load (TMDL) was implemented for the N-sensitive Neuse River Estuary (NRE), beginning in 1996, as an approach to reduce eutrophication and control the recurring large phytoplankton blooms and associated water quality and habitat degradation (harmful algal blooms, hypoxia/anoxia, fish kills). The TMDL mandated a 30% reduction in total N loading to the system and requires chlorophyll-a (Chl a) concentrations to be below 40 µg/L for 90% of samples collected (Session Laws 1995, Section 572). While reductions in dissolved inorganic N (DIN) loading have taken place (Lebo et al., 2012), nuisance phytoplankton blooms and high Chl a measurements persist (Paerl et al., 2009). The persistence of Chl a measurements above the 40 µg/L threshold could be a reflection of the changing forms of N. Despite a documented reduction in DIN, dissolved organic N (DON) has been increasing in the NRE over the past 20 years (Lebo et al., 2012). We hypothesize the increasing abundance of DON, specifically those sources related to the rapidly growing poultry operations and urbanization as reflected by septic outflow in rural, coastal NC, is sustaining the observed Chl a exceedances. The proposed study will conduct DON nutrient addition bioassays coupled with environmental surveys conducted in the NRE to research the link between changing N-sources, primarily as DON sources, to phytoplankton primary production and community composition. If results suggest these sources (poultry litter leachate, septic outflow, natural wetlands runoff) of DON stimulate phytoplankton primary productivity or select for harmful algal bloom taxa, then these bioreactive DON sources should be targeted in addition to DIN in efforts to control and mitigate the negative impacts of eutrophication on anthropogenically impacted N-sensitive coastal systems like the NRE.

Date: 05/01/15 - 4/30/19
Amount: $574,652.00
Funding Agencies: National Science Foundation (NSF)

Overview: Chromophoric dissolved organic matter (CDOM) is an important fraction of the marine carbon cycle that controls most light absorption and many photochemical and biological processes in the ocean. Despite its importance, the chemical basis for the formation of oceanic CDOM remains unclear. Laboratory studies support the paradigm that bacterial transformation of phytoplankton particulate organic matter (POM) and DOM produces the humic-like CDOM signals observed in the deep ocean. However, prior studies of oceanic CDOM using absorbance and fluorescence fit an electronic interaction (EI) model of intramolecular charge transfer (CT) reactions between donor and acceptor molecules common to partially-oxidized terrestrial molecules (e.g., lignin) found in humic substances. This proposal will test the hypothesis that phytoplankton and bacteria provide a source of donors (e.g., aromatic amino acids) and acceptors (quinones) which are microbially-transformed and linked, enabling CT contacts between them and creating oceanic CDOM. Hotspots for the formation of planktonic CDOM may be marine aggregates of phytoplankton detritus (marine snow). We will systematically study phytoplankton growth including marine snow formation, using roller bottles as a laboratory set-up that favors the formation of marine snow. A new technique of measuring base-extracted POM (BEPOM) absorbance and fluorescence will assist in testing fit of planktonic CDOM to the EI model, supplemented with measurement of its probable chemical precursors, thus explaining the production of CDOM in the ocean by linking the optics and chemistry of planktonic CDOM formation. Determining the time course and extent of phytoplankton POM and DOM transformation by heterotrophic bacterial (enzymatic hydrolysis) during the same phytoplankton growth experiments will provide an in-depth understanding as to how bacterial transformation of marine snow-associated planktonic organic matter drives CDOM production throughout the ocean. Intellectual Merit: This work represents a mechanistic study that will improve our understanding of the role of phytoplankton as the major source of CDOM in the open ocean. The key merit of this proposal is testing the fit of the EI model to planktonic CDOM via examination of: 1) its fluorescent quantum yields, 2) wavelength dependence of its fluorescence emission, and 3) alteration of its absorbance and fluorescence after borohydride reduction. These results will determine if intramolecular charge transfer occurs between reduced aromatics derived from amino acids and microbially-sourced quinones. A second merit is quantifying the importance of aggregate formation for oceanic CDOM formation. One implication of these results is that biomolecules in phytoplankton as on land must undergo a microbially-mediated transformation prior to developing chemical structures that give rise to CDOM?s optical properties. Broader Impacts: The importance of planktonic CDOM is not restricted to oceanography and the knowledge gained in this project will transfer to limnology and aquatic biogeochemistry as a whole. This study will provide unequivocal evidence for the remote sensing community that the CDOM spectra in the open ocean (and some lakes) are derived from phytoplankton. Each PI will utilize data gained from their respective research in classroom instruction and student mentoring. Beyond the classroom, we will work the NCSU Science House and the Nature Research Center at the North Carolina Science Museum of Natural Sciences to connect this important research topic with the general public. Using results from the work proposed, we will develop an interactive multimedia module for public display entitled, ?Light and Life in the Ocean,? at the NC Museum of Natural Sciences. Visitors to the display will be able to modify light via computer interface and learn effects of light on the ocean ecosystem. This module will be complemented with demonstrations and presentations at the UNC-CH Science Expo, a yearly event that introduces over 8000 members of the general public to scientific research taking place at UNC. As is possible, the PIs will conduct live feeds of shipboard and laboratory activities via Skype to classes at elementary schools in the Raleigh area so students can ?Ask an Oceanographer? questions regarding the experience and importance of conducting oceanographic research at sea and in the laboratory.

Date: 08/15/14 - 12/31/18
Amount: $781,849.00
Funding Agencies: National Aeronautics & Space Administration (NASA)

The aim of this proposal is to optimize algorithms that integrate optical and chemical information of dissolved organic matter (DOM) based on proxies for the prediction of its flux from marshes to coastal waters through estuaries. Land use and climate are important drivers that strongly influence the transport and fate of coastal wetland DOM offshore and these transitional areas have also been recognized recently as important sinks in the global carbon pool, commonly referred to as ?blue carbon.? Coastal wetlands in Louisiana, (e.g., marsh-estuarine complexes such as Barataria Bay) show clear decreasing gradients of DOM quantified as dissolved organic carbon (DOC) and dissolved lignin that suggest loss of blue carbon from the marshes to the more estuarine bays and subsequent export to coastal waters. The overarching hypothesis of this study is that changes to DOM chemistry within the marsh-estuarine complex imparts seasonal variability in the quantity and quality of DOM exported to the coastal ocean. This hypothesis is important to test because DOM reactivity to sunlight and/or bacteria regenerates mineral nutrients and CO2. Light-absorbing DOM (i.e., CDOM) also is a function of its chemistry, allowing CDOM retrievals from remote sensing reflectances to predict DOM quantity. The next step in the advancement of our understanding of the terrestrial-marine linkage?and the potential loss of blue carbon from coastal wetlands?is to predict DOM quality synoptically with remote sensing. We propose to test our hypothesis by combining co-varying chemical (dissolved lignin, stable isotopes) and optical (fluorescence) biomarkers that can deconvolve complex mixtures of DOM sources, along with optical measurements relatable to remote sensing observations. We plan to conduct seasonal (spring and fall) field campaigns in the Barataria Bay to modify existing algorithms for the VIIRS sensor, building on prior NASA-funded CDOM work by our team as part of the OCB and NACP programs. Coastal wetlands are economic powerhouses, supporting local fisheries productivity, recreation, aesthetics ? and their protection is a critical coastal management issue. Along the Gulf Coast of the United States, coastal wetlands are some of the most critically sensitive ecosystems under threat from anthropogenic and climatic stressors, particularly along the Louisiana coast. The Barataria Basin contains swamps, fresh, brackish, and saline marshes and bayous, in addition to the estuarine Bay proper, and serves as an ideal study site. The region has been heavily impacted from human modification such as subsidence, reduction of marshes from eustatic sea level rise, hurricanes, loss of resupply of materials from rivers due to channelization and construction of artificial levees. This proposal specifically addresses Item 3.2 Theme 2 related to carbon dynamics along the terrestrial-aquatic interface. Together, DOM chemical and optical properties can distinguish between terrestrial, marsh, and estuarine vegetation. Substantial variability exists in the sea-to-air fluxes of CO2 that likely is linked to the fate of blue carbon DOM in coastal waters as contributed by coastal wetlands. Remote sensing estimates of these sources obviously would improve our understanding of the role that coastal wetlands play in the contribution of continental margin systems to global carbon budgets, especially with respect to changing patterns of climate and land use. Quantifying the exchange of DOC between wetlands and shelf regions is critical to do now, especially in light of the impending rise of sea level will alter these fluxes; particularly in regions like Louisiana where relative sea level rise (RSLR) and wetland loss rates are considerably higher than other regions in the country. This information gap will be addressed with the proposed work.

Date: 11/01/16 - 12/31/17
Amount: $84,257.00
Funding Agencies: National Science Foundation (NSF)

Extreme weather events -- such as the record rainfall and massive flooding recently experienced along the southeast and mid-Atlantic US coasts from Hurricane Matthew -- are becoming more frequent and occurring with greater intensity. The importance of these events for coastal ocean biogeochemistry remain largely unknown because while events such as tropical storms are ephemeral, last perhaps a few days to a week, their effects on coastal environments last perhaps for multiple years to decades. During a storm, it can be very difficult (and life-threatening) to sample, yet the response of coastal ecosystems to an event can be observed and provide critical information and understanding regarding the spatial extent and magnitude of material fluxes of bioactive elements such as carbon (C) and nitrogen (N) to the coastal ocean. This is the purpose of our RAPID proposal. Amidst the chaos of such extreme events and their resulting effects on natural and human ecosystems, clear imperative biogeochemical questions emerge regarding these “hot moments”. For example, 1) How do coastal C and N budgets respond to floodwaters from tropical storms and hurricanes? 2) What is the biological and photochemical reactivity of this material? The first question can be answered via a relatively short, yet intense, period of observations, such as we propose here. The second question, which has potential teleconnections to climate in terms of CO2 fluxes, food web responses, and other ecosystems processes, requires a longer duration study. However, Question 2 could be answered by further study of samples collected during a short and intense period of sampling proposed to answer Question 1. In this RAPID proposal, we aim to improve our understanding of how estuaries and coastal systems respond to extreme events by measuring carbon and nutrient (N and P) loading into the Neuse River Estuary-Pamlico Sound (NRE-PS) coastal ecosystem. The NRE-PS is the urgent study site to examine resulting effects of Hurricane Matthew on coastal environments because it is downstream of the most intense flooding that occurred. Furthermore, it is the focus of a long-term monitoring program in that system, the Neuse River Estuary Modeling and Monitoring Program (ModMon), which was initiated in 1993. That date is significant because it preceded a recent rise in Atlantic tropical cyclone activity and has been able to capture the biogeochemical and ecological effects of major storms that have impacted the NC coast, including Hurricanes Fran (1996), Floyd (1999), Isabel (2003), Irene (2011). Incorporating Matthew will enable a comparison of these storms to the historic record. We propose to estimate fluxes and reservoirs of key constituents such as dissolved inorganic carbon (DIC), dissolved and particulate organic carbon and nitrogen (DOC, POC, DON, PON), and N and P nutrients, as well as chlorophyll biomass and pigment analyses. What this information will provide is a critical snapshot of the material fluxes into this coastal environment resulting from a major tropical storm and provide a comparison across spatiotemporal dimensions of the NRE-PS and other coastal environments such as the Chesapeake Bay, Mississippi River plume, etc.

Date: 04/15/16 - 10/30/16
Amount: $5,000.00
Funding Agencies: NCSU Sea Grant Program

Urbanized estuaries such as many of the tidal creeks along the NC coastline are suffering from poor water quality and exhibit greater fluctuations in dissolved oxygen saturation (%DO) and pH. Tight relationships between %DO and pH indicate strong heterotrophy in these ecosystems caused by inputs of readily respirable organic carbon (OC). While primary production can be a key input of OC to estuaries, so too can runoff from urbanized catchments. Globally this effect of eutrophication and urbanization has been shown to cause severe undersaturation of aragonite which can impact the health and survivability of economically and ecologically valuable marine life such as oysters (Feely et al. 2010). Urbanization in coastal watersheds threatens ecosystem health by increasing nutrient and dissolved organic matter (DOM) loads to estuarine ecosystems such as tidal creeks which serve as important habitat for shellfish (Fig. A1). When DOM is respired by estuarine bacteria, dissolved oxygen (DO) concentrations decrease, leading to hypoxia and an accumulation of carbon dioxide (CO2) as OC decreases. This increase in the partial pressure of CO2 in coastal waters increases the amount of carbonic acid in these waters, which leads to decreases in pH (Cai et al. 2011; Duarte et al. 2011; Wallace et al. 2014). While these changes occur naturally in estuarine systems, eutrophication and urbanization contribute to increases in the magnitude and duration of hypoxia and low pH conditions (Ringwood and Keppler, 2002). An example is provided in Figure A2 for Hoop Pole Creek near Morehead City, NC. The most severe fluctuations in this small urbanized estuary occur near a stormwater discharge. Tidal creeks impacted by urbanization are thus subject to large fluctuations in DO and pH, and “coastal ocean acidification” (COA) is increasing for estuarine waters in part because of greater inputs of DOM (Nixon 1995; Cai et al 2011). Despite high rates of primary production that fix CO2 (providing an estuarine “sink” of CO2) and produce DO, the organic matter produced is readily consumed by microbes and adds to the heterotrophy of estuarine and coastal waters (Diaz and Rosenberg 1995). Recent evidence shows that DOM from urbanized catchments are structurally distinct from natural (e.g., forested) catchments and have higher bioavailability to heterotrophs (Seitzinger et al. 2002). Warmer temperatures related to global warming are likely to further exacerbate these conditions due to decreased solubility of oxygen and increased microbial respiration rates. DOM quality as well as quantity released from sediments in tidal creek estuaries is a central component of this study because the compounds comprising the DOM load (i.e., its quality) is a function of the land uses within its watershed. While it is known that urban DOM is more bioavailable than terrestrial DOM (Seitzinger et al. 2002; Wiegner et al. 2006; Petrone et al. 2009; Parr et al. 2015), an overlooked source of bioavailable urban DOM is its release from urban particulate organic matter (POM) deposited in estuarine sediments. Runoff from urbanized estuaries contains OM from sewage and septic systems, industrial and residential wastes, etc. all of which change the quality of the OM delivered to estuarine sediments, and contribute highly bioavailable DOM to estuarine organisms (Seitzsinger et al. 2002; Feely et al. 2010; Wallace et al. 2014). These anthropogenic sources are enriched in compounds readily utilized by estuarine bacteria during heterotrophic respiration once the sedimentary OM is released as DOM. Excessive organic nutrient loading in bottom waters accelerates eutrophication and can lead to estuarine hypoxia and anoxia as microbial populations consume DOM and respire it as CO2, thereby driving the carbonate system toward carbonic acid and resulting in reduced pH. Further, it is proposed that the accumulation of bioavailable sedimentary organic matter during the winter when microbial degradation and respiration are low will be greater in more urbanized settings. These large winter stores of bioavailable DOM will then fuel microbial respiration during the spring and summer resulting in even higher CO2 levels and more severe COA.

Date: 09/15/11 - 9/14/16
Amount: $784,477.00
Funding Agencies: US Dept. of Energy (DOE)

The proposed work would quantitatively investigate the impact of regional, interbasin groundwater flow on watershed carbon budgets at an AmeriFlux research site in the tropical rainforest of Costa Rica (La Selva Biological Station). An overarching theme of the work is that accurate understanding of ecosystem carbon budgets will, at La Selva and likely at other sites, be improved by considering the eddy covariance data in combination with hydrologic fluxes of carbon (in this case, a large flux of carbon from upward discharge of old, regional groundwater into the site from below). Tropical forests contain critical components of the global carbon cycle, including high primary productivity, large stores of above-ground biomass and soil carbon, and the dissolved carbon both transported in and degassed from tropical streams and rivers. In a recent major review and synthesis paper on the carbon cycle in inland (terrestrial) waters, two of the most pressing research needs identified by Cole et al. (2007) were: 1. the role of groundwater in sequestering, transporting, and releasing carbon, and 2. the potential significance of small streams and lakes in degassing CO2. These suggestions from Cole et al. (2007) are closely aligned with our preliminary results suggesting a strong link between regional interbasin groundwater flow and carbon cycling in the lowland rainforest at La Selva. Interbasin groundwater flow (IGF) is groundwater flow beneath topographic watershed divides, recharged in one watershed and discharged in another. IGF is a basic groundwater process that has been detected at watersheds world-wide, and is often a major influence on the quantity and quality of water in watersheds. There is an increasing awareness of the significance of IGF for climate. Regional- to continental-scale water and energy transport via IGF should be considered in large-scale climate models (Schaller and Fan 2009), and groundwater convergence in major discharge zones (e.g., gaining watersheds that receive IGF) may play a role in the persistence of multi-year precipitation anomalies (Bierkens and van den Hurk 2007). The links between IGF, carbon cycling, and climate are relatively unexplored but potentially significant. Recent data from La Selva suggest that IGF: (1) carries a significant quantity of isotopically and chemically distinct dissolved carbon into the rainforest (an amount roughly equal to the upper limit on net ecosystem exchange (NEE) of CO2 with the atmosphere at this site), (2) reduces concentrations of dissolved organic carbon (DOC) in streams while increasing those of dissolved inorganic carbon (DIC), and (3) increases watershed export of dissolved carbon by streams. The effect of IGF on the rate of CO2 degassing from affected watersheds is currently unknown. Our proposed work lies at the unexplored but potentially significant intersection of IGF and carbon cycling in tropical forests. We will use new data (carbon concentrations in streams and groundwater, chemical and isotopic characteristics, NEE from eddy covariance, CO2 degassing rates in streams, soil respiration, stream discharge), in the context of a paired-watershed approach (one watershed with significant inputs by IGF, and the other without), to quantify the influence of IGF on hydrologic fluxes of carbon, the overall carbon budgets of these tropical forest watersheds, and the potential for transfer of ?old? carbon from regional groundwater (IGF) into modern carbon cycles. Also, we will determine whether ?old? DOC from IGF is relatively ?protected? from biological degradation, thus facilitating its hydrologic export from the watershed. Thus, the project will quantitatively explore the importance, for carbon cycling and ecosystem or watershed carbon budgets, of the link between the tropical rainforest and the deeper hydrogeological system on which it sits. With IGF as a central organizing theme, the proposed work will by design have direct relevance to the question of whether the tropical forest watersheds under study are net sinks or sourc

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